The ideal for me would have been more spells and all of them open world with some totem/carnival for the hard to place ones(having them available in instances as well is great if you don't wanna compete with others on a busy spot). As for the rng, I despise it in group content, so I won't even touch the trials ones. But if they were all open world I wouldn't mind them being a bit slower, almost all of my overworld ones I learnt in 2-5 kills. I wouldn't mind if they split the difference and some of the spells were in the 20-30 kills range (for mobs that have multiple spawn locations around the world).